Can I install the VSP Engine Tools on a standalone server site?

Yes, you can do so if you define an appropriate ArcGIS Server connection file in the VSP Engine Tools post installer. However, for integration into other VertiGIS Products such as VertiGIS Studio Web you will need to have the VSP Engine Tools published on an ArcGIS Server federated with a Portal. The option for installing on a standalone server should only be selected for VSP Engine Tools integration in legacy VertiGIS Products such as WebOffice, or for other custom setup requirements.